Device for absorbing floor-landing shock for legged mobile robot

ABSTRACT

A landing shock absorbing device  18  disposed in a foot mechanism  6  of a leg of a robot, wherein an inflatable bag-like member  19  (variable capacity element) is provided at a bottom face side of the foot mechanism  6 . The bag-like member  19  is constructed of an elastic material such as rubber. The air in atmosphere may flow into and out of the bag-like member  19  by inflow/outflow means  20  equipped with a solenoid valve  27 , and the like. In a lifting state of the foot mechanism  6 , inflow of the air into the bag-like member  19  is controlled, thereby controlling the final height of the bag-like member  19  in an inflated state to the height in response to a gait type of the robot. While properly reducing an impact load during a landing motion of the leg of a legged mobile robot depending on the gait type of the robot, stability of a posture of the robot may easily be secured, resulting in allowing a configuration to be lighter in weight.

TECHNICAL FIELD

The present invention relates to a landing shock absorber for reducingan impact load during a landing motion of a leg of a legged mobilerobot.

BACKGROUND ART

In a legged mobile robot such as a biped mobile robot equipped with aplurality of legs, each leg is brought into contact with a floor througha ground-contacting face portion of a foot mechanism provided on a farend portion thereof. More particularly, the foot mechanism is amechanism connected to a joint on the farthest end side of each leg (anankle joint). The legged mobile robot moves by lifting and landingmotions of each leg. More particularly, the lifting and landing motionsare a repetition of motions that while at least one leg of a pluralityof legs as a supporting leg maintains a foot mechanism of the supportingleg in a ground-contacting state, the other leg as a free leg lifts afoot mechanism of the free leg from its ground-contacting location intothe air and moves the same, and makes contact with the ground on otherground-contacting location.

In such a legged mobile robot, when a ground-contacting face portion ofa foot mechanism of the leg is brought into contact with the ground bythe landing motion of each leg, a relatively high impact load (atransient floor reaction force) instantaneously acts through the footmechanism of the leg. Particularly, when the legged mobile robot ismoved at relatively high moving speed, motion energy of the leg inmoments immediately before the foot mechanism of the leg makes contactwith the ground is great, so that the impact load will be high. Whenthis impact load is high, rigidity of each portion of each leg needs tobe enhanced in order to resist the load, and furthermore, this willinterfere with a size reduction and a weight reduction of each leg.Accordingly, a reduction (shock absorption) of such an impact load isdesired.

As such a shock absorber, for example, the one that the presentapplicant proposed in Japanese Patent Laid-Open Publication No.5-305578is known. In this shock absorber, a cylinder filled with hydraulic oilis provided at a heel of the foot mechanism, and a rod is extendedlyprovided from a piston slidable in this cylinder toward a bottom faceside of the heel of the foot mechanism. A ground-contacting elementwidened in diameter in a mushroom shape is provided on a tip portion ofthe rod. Additionally, the piston is energized in a direction that theground-contacting element projects to the bottom face side of the footmechanism by a spring accommodated in the cylinder on the upper sidethereof. Furthermore, in the piston, a flow passage that allows thehydraulic oil to flow between an upper chamber and a lower chamberthereof is drilled.

In the shock absorber configured in this manner, at the time of thelanding motion of the leg, the aforementioned ground-contacting elementmakes contact with the ground and is pressed with the piston in adirection opposite to an energizing force of the spring. At this moment,while the hydraulic oil in the cylinder flows through the flow passageof the piston, the piston slides in a direction that the pistoncompresses the spring, and this allows the impact load during thelanding motion of the leg to be reduced.

However, in the shock absorber like this, a stroke of theground-contacting element after the ground-contacting element of eachleg makes contact with the ground until the foot mechanism of the legmakes contact with the ground is constant without depending on a gaittype such as moving speed of the robot, and resultingly, in some gaittypes of the robot, the shock absorber may not exert a shock absorbingeffect suitable for the gait type thereof. For instance, when the movingspeed of the robot is fast, an attenuation of motion energy of the footmechanism of the leg may occur too slow, or when the moving speed of therobot is slow, the attenuation of the motion energy of the footmechanism of the leg may occur too fast. Accordingly, it may bedifficult to smoothly secure stability of a posture of the robot.

Furthermore, in the shock absorber, as a result of the use of thehydraulic oil, weight of the shock absorber will be heavy, resulting ininterfering with a weight reduction of the robot. Additionally, theground-contacting element that makes contact with the ground during thelanding motion of the leg can only move in a sliding direction of thepiston (an axial center direction of the cylinder) and is a solid body.Consequently, the impact load acting on the ground-contacting elementmay act in a direction that crosses a movable direction thereofdepending on a geometry of a floor, so that the impact load may notadequately be reduced, and a damage of the shock absorber may begenerated.

In light of such a background, it is an object of the present inventionto provide a landing shock absorber that may easily secure stability ofa posture of a robot, while properly reducing an impact load during alanding motion of a leg of a legged mobile robot such as a biped mobilerobot in response to a gait type of the robot, and furthermore, may bewith a light-weight configuration.

DESCLOSURE OF INVENTION

To achieve such an object, a landing shock absorbing device of a leggedmobile robot of the present invention is characterized in that in thelegged mobile robot moving by lifting and landing motions of a pluralityof legs that can make contact with the ground through aground-contacting face portion of a foot mechanism, respectively, thereare a variable capacity element provided in the foot mechanism of theleg to be compressed by undergoing a floor reaction force during thelanding motion of each leg and to be inflatable when no longerundergoing the floor reaction force at least by the lifting motion ofthe leg, thereby allowing compressible fluid to flow into and flow outof an interior portion thereof with the inflation and the compressionthereof, and inflow/outflow means for flowing the compressible fluidinto the variable capacity element while inflating the variable capacityelement in a lifting state of each leg and flowing the compressiblefluid out of the variable capacity element with the compression of thevariable capacity element caused by the floor reaction force, thatoutflow resistance is generated during the outflow of the compressiblefluid in the variable capacity element by the inflow/outflow means, isequipped with inflation control means for controlling an inflow amountof the fluid into the variable capacity element by the inflow/outflowmeans depending on the gait type in order to change a size of thevariable capacity element in a compression direction to become apredetermined size depending on a gait type of the legged mobile robot,when the variable capacity element is inflated in the lifting state ofeach of the above-mentioned legs (a first invention).

Further, in the present invention, the landing motion of each leg meansa motion that the foot mechanism is moved down to allow theground-contacting face portion thereof to make contact with the groundfrom a state that the ground-contacting face portion of the footmechanism of the leg is left from a floor, and the lifting motion of theleg means a motion that the foot mechanism is lifted into the air toallow the ground-contacting face portion thereof to be left from thefloor from a state that the ground-contacting face portion of the footmechanism of the leg is put in contact with the floor. Additionally, thelifting state of each leg or the foot mechanism is a state of the leg ina free leg stage, and means a state that the ground-contacting faceportion of the foot mechanism of the leg is left from the floor.Furthermore, the landing state of each leg or the foot mechanism is astate of the leg in a supporting leg stage, and means a state that anentire portion or a portion of the ground-contacting face portion of thefoot mechanism of the leg is put in contact with the ground.

According to the present invention (the first invention), during thelanding motion of each leg, the variable capacity element in an inflatedstate is compressed, and at this time, the fluid in the variablecapacity element is flowed out of the variable capacity element by theinflow/outflow means with the outflow resistance. Accordingly, motionenergy of the leg for performing the landing motion is absorbed andmomentum of the foot mechanism of the leg is decreased, resulting inreducing an impact load acting on the leg during the landing motionthereof. In the present invention (the first invention), during thevariable capacity element in the lifting state of the leg is inflated,the inflation control means controls the inflow amount of the fluid intothe variable capacity element by the inflow/outflow means depending onthe gait type, so that the size of the variable capacity element in thecompression direction before the variable capacity element begins to becompressed by the landing motion of each leg will be controlled to bethe predetermined size depending on the gait type of the robot.Accordingly, a compressive amount of the variable capacity element bythe landing motion of each leg as well as an outflow amount of the fluidfrom the variable capacity element may be matched to the gait type ofthe robot (for example, a gait type such as moving speed). As a result,a shock absorbing effect of a landing shock by the landing shockabsorbing device of the present invention (the first invention) may beadapted to be suitable for the gait type of the robot. In other words, atransient change of a floor reaction force acting on the leg during thelanding motion of each leg may be adapted to be suitable for the gaittype of the robot, and then stabilization of a posture of the robot mayproperly be planned.

Further, as the moving speed of the robot increases, commonly, the sizeof the variable capacity element in the compression direction before thelanding motion of each leg is preferably increased. In this manner, aflow rate of the fluid flowing out of the variable capacity element at atime that the variable capacity element is compressed increases andoutflow resistance thereof increases, and resultingly, a damping effectof the landing shock absorbing device (an attenuating effect of motionenergy) may be enhanced.

In the present invention as described above (the first invention), it ispreferable that the fluid comprises a compressible fluid (a secondinvention). Specifically, since the compressible fluid has a springproperty, a part of motion energy of the leg is converted into elasticenergy of the compressible fluid inside of the variable capacity elementin the landing motion of each leg. Then, the elastic energy dissipatesby the outflow resistance in the process in which the compressible fluidflows out of the variable capacity element with the compression of thevariable capacity element. As a result, in the landing motion of eachleg, the impact load (hereinafter, it may be referred to as a landingshock) can be effectively reduced while avoiding an instantaneous rapidchange in the floor reaction force acting on the leg through thevariable capacity element and the compressible fluid inside of thevariable capacity element.

As the compressible fluid, a gas such as air, liquid containing airbubbles, gel or the like is exemplified. In this case, particularly inthe case where a gas is used as the compressible fluid, the compressiblefluid becomes lightweight, whereby the landing shock absorbing device ofthe present invention can be lightweight.

The present invention using the compressible fluid as described above(the second invention) is preferable in the case where the legged mobilerobot is a robot that a position and a posture of the foot mechanism arecontrolled by compliance control so as to allow a moment about an axisin a horizontal direction for the floor reaction force acting on thefoot mechanism of each leg to follow a predetermined desired moment (athird invention). That is to say, since a spring constant of thecompressible fluid is decreased due to the compression of the variablecapacity element by the landing motion of the leg, a gain of the control(compliance gain) can be increased while securing stability of a controlsystem of the compliance control. As a result, the following—property ofthe moment about the axis in the horizontal direction acting on each ofthe foot mechanisms to the desired moment can be enhanced. Accordingly,posture stability of the robot can be secured while properly reducingthe impact load when landing the floor.

Furthermore, in the present invention (the first through thirdinventions), it is preferable that the variable capacity element isconstructed of a deformable bag-like member provided on a bottom faceside of the foot mechanism of the leg to make contact with the groundahead of the ground-contacting face portion of the foot mechanism of theleg during the landing motion of each leg (a fourth invention). That isto say, the bag-like member makes contact with the ground ahead of theground-contacting face portion of the foot mechanism of the leg in thelanding motion of each leg and is compressed. At this time, since thebag-like member can be deformed along a surface geometry of the floor, ashock absorbing function of the landing shock absorbing device of thepresent invention can be exerted regardless of the geometry of the flooror the like as long as the bag-like member can make contact with theground. Accordingly, reliability of reduction effect of the impact loadduring the landing motion of the leg can be enhanced. Furthermore, sincethe bag-like member has a high flexibility in deformation, the situationof damaging the bag-like member can be avoided even when the floorreaction force acts on the bag-like member from various directions inthe landing motion of each leg.

Additionally, in the present invention (the first through the fourthinventions), the inflation control means judges whether or not the sizeof the variable capacity element in a compression direction is inflatedto the predetermined size based on inflow time of the fluid into thevariable capacity element in the lifting state of each of the legs, andwhen the size of the variable capacity element is judged to be inflatedto the predetermined size, blocks the inflow of the fluid into thevariable capacity element by the inflow/outflow means (a fifthinvention). Accordingly, the variable capacity element may be controlledwith a relatively simple configuration without requiring a sensor or thelike.

Alternatively, the landing shock absorbing device comprises a sensor fordetecting a physical quantity varied depending on the size of thevariable capacity element in the compression direction, and theinflation control means judges whether or not the size of the variablecapacity element in the compression direction is inflated to thepredetermined size based on detection data of the sensor, and whenjudging that the size of the variable capacity element in thecompression direction is inflated to the predetermined size, inflationcontrol means blocks off the inflow of the fluid into the variablecapacity element by the inflow/outflow means (a sixth invention).According to this, the final size of the variable capacity element inthe compression direction when inflating the variable capacity elementin the lifting state of each leg can be reliably controlled to thepredetermined size according to the gait types.

Furthermore, in the present invention (the first through the sixthinventions), a sensor for detecting whether or not the ground-contactingface portion of the foot mechanism of each of the legs is in contactwith the ground is provided, and the inflation control means preferablycontrols the inflow of the fluid into the variable capacity element bythe inflow/outflow means to increase the size of the variable capacityelement in the compression direction, when a ground-contact of theground-contacting face portion of the foot mechanism is not detected bythe sensor at a planned time for landing each leg defined depending ondesired gaits of the legged mobile robot (a planned time that the footmechanism of each leg makes contact with the ground through theground-contacting face portion thereof) (a seventh invention).

In other words, when the ground-contact of the ground-contacting faceportion of the foot mechanism is not detected by the sensor at theplanned time for landing each leg, in order to perform a motion of therobot subsequent to that, the foot mechanism of the leg needs topromptly be brought in contact with the floor. In this situation, whenthe foot mechanism is actually put into contact with the floor, theimpact load acting on the leg tends to be high. Therefore, in thepresent invention, in such a situation, the inflow of the fluid into thevariable capacity element by the inflow/outflow means is controlled toincrease the size of the variable capacity element in the compressiondirection as described above. Accordingly, a possible compressive amountof the variable capacity element increases, so that the impact load at atime that the foot mechanism actually makes contact with the ground mayproperly be reduced.

Additionally, in the present invention (the first through the fourthinventions), a sensor for detecting a size of the variable capacityelement in the compression direction is provided, and the inflationcontrol means sets a time-varying pattern of a desired size of thevariable capacity element in the compression direction depending on thegait type of the legged mobile robot at a time that the variablecapacity element is inflated, and controls the inflow and the outflow ofthe fluid of the variable capacity element by the inflow/outflow meansin such a manner that the size of the variable capacity element in thecompression direction detected by the sensor is changed according to thetime-varying pattern of the desired size (an eighth invention).

This allows the size of the variable capacity element in the compressiondirection to successively be controlled to be suitable for the gaittypes of the robot. Consequently, the shock absorbing effect by thelanding shock absorbing device of the present invention as well as aneffect for the stabilization of the posture of the robot may beenhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a basic configuration of a legged mobilerobot in an embodiment of the present invention,

FIG. 2 is a cross-sectional view showing a side face of a foot mechanismprovided with a landing shock absorbing device of a first embodiment ofthe present invention,

FIG. 3 is a plan view viewed from a bottom face side of the footmechanism of FIG. 2,

FIG. 4 is a flowchart showing processing for a motion control of thelegged mobile robot of FIG. 1,

FIG. 5 is a flowchart for explaining an operation of the landing shockabsorbing device of the foot mechanism in FIG. 2, and

FIG. 6 is a timing chart for explaining the operation of the landingshock absorbing device of the foot mechanism in FIG. 2.

FIG. 7 is a flowchart for explaining an operation of a landing shockabsorbing device of a second embodiment of the present invention,

FIG. 8 is an exemplary view of a substantial part of a foot mechanismprovided with a landing shock absorbing device of a third embodiment ofthe present invention,

FIG. 9 is a flowchart for explaining an operation of the landing shockabsorbing device of the third embodiment of the present invention, and

FIG. 10 is a flowchart for explaining an operation of a landing shockabsorbing device of a fourth embodiment of the present invention.

FIG. 11 is an exemplary view of a substantial part of a foot mechanismin a modified aspect relating to the first through fourth embodiments ofthe present invention, and

FIG. 12 is an exemplary view of a substantial part of a foot mechanismin a modified aspect relating to the first through fourth embodiments ofthe present invention.

FIG. 13 is an exemplary view of a substantial part of a foot mechanismprovided with a landing shock absorbing device of a fifth embodiment ofthe present invention,

FIG. 14 is a flowchart for explaining an operation of the landing shockabsorbing device of the foot mechanism in FIG. 13,

FIG. 15 are timing charts for explaining the operations of the landingshock absorbing device of the foot mechanism in FIG. 13, and

FIG. 16 is a cross-sectional view of a side face of a foot mechanismprovided with a landing shock absorbing device of a sixth embodiment ofthe present invention.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1 through 6, a first embodiment of the presentinvention is described. FIG. 1 is a side view showing an overall basicconfiguration of a legged mobile robot of the present embodiment inschematic form. As shown in FIG. 1, for example, the legged mobile robot1 of the present embodiment is a biped mobile robot comprising a pair of(two) legs 3, 3 extendedly disposed from a lower end portion of itsupper body 2 (torso). Further, arms and a head may be attached on theupper body 2.

Each leg 3 is constructed by connecting a thigh 4, a lower leg 5, and afoot mechanism 6 in the order listed through a hip joint 7, a knee joint8, and an ankle joint 9 from the lower end portion of the upper body 2.More specifically, each leg 3 is adapted to be configured with the thigh4 extendedly disposed from the lower end portion of the upper body 2through the hip joint 7, the lower leg 5 connected to a far end portionof the thigh 4 through the knee joint 8, and the foot mechanism 6connected to a far end portion of the lower leg 5 through the anklejoint 9. Each leg 3 can be brought into contact with a floor A throughthe foot mechanism 6 presented on a distal end side thereof, andsupports the upper body 2 by this ground contact. In this situation, thehip joint 7 of each leg 3 is adapted to be capable of rotary motionsabout three axes in an upward/downward direction, a forward/backwarddirection, and a right/left direction, the knee joint 8 is adapted to becapable of a rotary motion about one axis in the right/left direction,and the ankle joint 9 is adapted to be capable of rotary motions of twoaxes in the forward/backward direction and the right/left direction ofthe robot 1. According to the rotary motions of respective joints 7through 9, each leg 3 is adapted to be capable of performing a movementsubstantially the same as a human leg.

Additionally, the respective joints 7 through 9 of each leg 3 isprovided with an electric motor (not shown) as an actuator forperforming the rotary motion about each axis. Furthermore, the upperbody 2 of the robot 1 is equipped with a controller 10 for controllingmotions of the legs 3, 3 of the robot 1 (a motion control for theelectric motor of the respective joints 7 through 9), and a battery 11as an electric source for a motion of the robot 1, etc. The controller10 is constructed of an electric circuit including a microcomputer, etc.In this situation, in moving the robot 1, the controller 10 attempts tomove the robot 1 like a human by alternately repeating a lifting and alanding motions for the two legs 3, 3. More specifically, a repetitionof the lifting and landing motions is an action as follows. In otherwords, either one of the two legs 3, 3 is taken as a supporting leg andthe other as a free leg. In a state that the leg 3 on a supporting legside is landed on the floor (the foot mechanism 6 of the leg 3 isbrought into contact with the floor A), the leg 3 on a free leg side islifted (the foot mechanism 6 of the leg 3 is lifted from the floor Ainto the air). Furthermore, the lifted foot mechanism 6 of the leg 3 onthe free leg side is moved in the air, and then landed on a desiredplace. The landed leg 3 on the free leg side is, then, newly taken asthe supporting leg and the leg 3 which has been taken as the supportingleg is newly taken as the free leg, and the leg 3 newly taken as thefree leg is moved as described above. Such a repetition of the motion ofthe legs 3, 3 is the repetition of the lifting and landing motions ofthe legs 3, 3 during the movement of the robot 1.

Referring to FIG. 2 and FIG. 3, a configuration of the foot mechanism 6of each leg 3 is further described. FIG. 2 is a cross-sectional viewshowing a side face of the foot mechanism 6, and FIG. 3 is a plan viewviewed from a bottom face side of the foot mechanism 6.

The foot mechanism 6 is provided with a foot plate member 12 in agenerally tabular form as a skeletal member. The foot plate member 12 isdesigned with its front end portion (toe portion) and its rear endportion (heel portion) each curved slightly upward, but otherwise in aflat tabular form. In addition, on a top face portion of the foot platemember 12, a tube member 13 in a cross-sectionally rectangular form isfixedly provided with its axis in a vertical direction. Inside of thetube member 13, a movable plate 14, which is disposed to be movablesubstantially in the vertical direction to be arranged along an innercircumferential surface of the tube member 13, is provided and themovable plate 14 is connected to the ankle joint 9 through a six-axisforce sensor 15. The six-axis force sensor 15 detects a floor reactionforce acting on the foot mechanism 6 (specifically, a translationalforce of three axis directions in a forward/backward direction, aright/left direction, and an upward/downward direction, and moment aboutthree axes), and its detected output is input into the controller 10.

Additionally, the movable plate 14 is connected to the top face portionof the foot plate member 12 through a plurality of elastic members 16(described as a spring in FIG. 2) with a peripheral portion of its lowerface constructed of a spring, rubber, or the like. Therefore, the footplate member 12 is connected to the ankle joint 9 through the elasticmember 16, the movable plate 14 and the six-axis force sensor 15.Further, the interior portion of the tube member 13 (a space under themovable plate 14) is opened to an atmospheric side through a hole or agap which is not shown, so that the air in the atmosphere can freelycome into and go out of the interior portion of the tube member 13.

Ground-contacting members 17 are attached to the bottom face (the lowerface) of the foot plate member 12. The ground-contacting members 17 areelastic members intervened between the foot plate member 12 and thefloor when the foot mechanism 6 is landed (an elastic member thatdirectly makes contact with the floor), and fixed to four corners of theground-contacting surface of the foot plate member 12 (both sides of thetoe portion and both sides of the heel portion of the foot plate member12) in the present embodiment. Additionally, in the present embodiment,the ground-contacting members 17 are formed in a two-layer structure inwhich a soft layer 17 a made of a relatively soft rubber material and ahard layer 17 b made of a relatively hard rubber material are verticallypolymerized, and the hard layer 17 b is provided on the lowest face sidethereof as a ground-contacting face portion directly making contact withthe floor during the landing of the leg 3.

The foot mechanism 6 is provided with a landing shock absorbing device18 associated with the present invention in addition to the aboveconfiguration. The landing shock absorbing device 18 is provided with abag-like member 19 attached to the bottom face of the foot plate member12, and inflow/outflow means 20 for flowing the air (the air in theatmosphere) as compressible fluid into and out of the interior portionof the bag-like member 19.

The bag-like member 19 is provided substantially in the center portionof the bottom face of the foot plate member 12 in such a manner that theground-contacting members 17 are presented around a periphery thereof.This bag-like member 19 is deformably structured of an elastic materialsuch as rubber or the like, so that an upwardly opened barrel-typecontainer shape with a bottom is presented as shown in FIG. 2 in anatural state that an elastic deformation is not generated by externalforces. The bag-like member 19 is designed with all the opened endportion thereof being firmly fixed on the bottom face of the foot platemember 12 and being shut and covered with the foot plate member 12.Additionally, in a natural state that the bag-like member 19 ispresented in the barrel-type container shape with a bottom, the bottomface of the bag-like member 19 is provided to protrude lower than theground-contacting members 17. In other words, a height of the bag-likemember 19 (a distance from the lower face of foot plate member 12 to thebottom face of the bag-like member 19) is adapted to be taller than athickness of the ground-contacting members 17. Accordingly, in a statethat the foot plate member 12 is brought into contact with the groundthrough the ground-contacting members 17 (the landing state of the leg3), the bag-like member 19 is compressed in a height direction of thebag-like member 19 by a floor reaction force, as shown about the leg 3in the landing state in FIG. 1 (the leg 3 on a forward side of the robot1 in FIG. 1).

The natural state that the bag-like member 19 is presented in thebarrel-type container shape with a bottom is an inflated state of thebag-like member 19 and in this inflated state, the bag-like member isfilled with air under a pressure equivalent to the atmospheric pressurethrough the inflow/outflow means 20 described below. The bag-like member19 is constructed of the elastic material, resulting in having a shaperestoring force into a shape in the natural state (the barrel-typecontainer shape with a bottom) when compressed. The shape of thebag-like member 19 in the natural state does not always need to bebarrel type, but may be a cylindrical shape with a bottom, for example.

The inflow/outflow means 20 is provided with two flow holes (flowpassages) 21 and 22 drilled in the foot plate member 12 so as tocommunicatively connect the interior portion of the bag-like member 19and the interior portion of the tube member 13, and fluid conduits 23and 24 (flow passages) connected to the respective flow holes 21 and 22inside of the tube member 13 and led to the outside of the tube member13. Far end portions of these fluid conduits 23 and 24 (ends on theopposite side of the bag-like member 19) are opened to the atmosphere.In addition, the fluid conduit 23 is provided with a check valve 25 forblocking air from flowing into the bag-like member through the conduit.Furthermore, the fluid conduit 24 is provided with a check valve 26 forblocking air in the bag-like member 19 from flowing out through theconduit, and a solenoid valve 27 capable of being controlled for openingand closing by the controller 10. Here, in FIG. 2, for convenience, thefluid conduits 23 and 24, and the check valves 25 and 26 and thesolenoid valve 27 which are provided in the conduits are illustrated asthey are provided away from the foot mechanism 6 or the like. However,these are actually attached in a proper place of the leg 3 such as thefoot mechanism 6, or housed inside of the tube member 13. According tothe present embodiment, the flow holes 21 and 22 are throttled passages,and an opening area of the flow hole 21 is smaller than that of the flowhole 22.

In the inflow/outflow means 20 configured in this manner, when thebag-like member 19 is compressed, air in the bag-like member 19 flowsout to the atmosphere through the flow hole 21 and the fluid conduit 23.Furthermore, in a state that the solenoid valve 27 is opened, air in theatmosphere flows into the bag-like member 19 through the fluid conduit24 and the flow hole 22 as the bag-like member 19 inflates from thecompressed state to the natural state by the shape restoring force. Inaddition, when the air flows in and out with respect to the bag-likemember 19, fluid resistance is generated by the flow holes 21 and 22 asthe throttled passages. In this case, since the opening area of the flowhole 21 is smaller, the outflow resistance of the air from the bag-likemember 19 is relatively large. In contrast, since the opening area ofthe flow hole 22 is relatively large, inflow resistance of the air tothe bag-like member 19 is relatively small.

The solenoid valve 27 in conjunction with the controller 10 forperforming the opening and closing control thereon constitutes inflationcontrol means in the present invention.

Subsequently, in the present embodiment, a basic motion control of theleg 3 for moving the robot 1 is described. Further, this motion control(processing other than that in STEP 6 in FIG. 4) is described in detailin Japanese Patent Laid-Open Publication No. 10-277969, etc. by thepresent applicant, and hence, only a summary is described herein.

The controller 10 equipped on the upper body 2 of the robot 1 executesprocessing shown in a flowchart of FIG. 4 by a predetermined controlcycle. In other words, the controller 10 first judges whether or notswitching timing is presented for a gait (a walking pattern of the leg3) of the robot 1 (STEP 1). Here, the switching timing of the gait isswitching timing of a supporting leg, and timing when the leg 3 on thefree leg side lands on the floor (when the bag-like member 19 of thefoot mechanism 6 of the leg 3 makes contact with the ground in thepresent embodiment) for example. The judgment for this timing is madebased on output of the six-axis force sensor 15 or the like for example.

When the switching timing for the gait is presented in STEP 1, afterinitializing control processing time t to “0” (STEP 2), the controller10 updates a gait parameter (STEP 3) based on a motion command of therobot 1 externally given and a predetermined movement plan of the robot1 (a plan prescribed what timing is taken and how the robot 1 is moved,etc.). Here, the gait parameter is a parameter for defining a desiredgait for one walking step of the robot 1 and for example, it is aparameter for movement modes of walking, running, and the like, lengthof a step while the robot 1 is moving, a moving speed (walking cycle),or the like. In addition, the desired gait of the robot 1 is constructedof a desired position and a trajectory of a posture of the upper body 2,a desired position and a trajectory of a posture of the foot mechanism 6of each leg 3, a desired total floor reaction force (a desired value fora resultant force of a floor reaction force each acting on both the legs3, 3), a trajectory of a desired ZMP (a desired position of an actingpoint for the total floor reaction force), and the like. Further, thedesired ZMP is more specifically a desired position of an acting pointfor a total floor reaction force to dynamically counterpoise with aresultant force of an inertia force and gravity acting on the robot 1depending on a desired motion pattern of the robot 1 defined accordingto the desired position and the trajectory of the posture of the upperbody 2 as well as the desired position and the trajectory of the postureof the foot mechanism 6 of each leg 3 (a total floor reaction force onthe same line of action with the resultant force), and a desiredposition for a point on the floor in such a way that moments (a momentabout an axis of a horizontal direction) except a moment about an axisof a vertical direction for the total floor reaction force become “0”(Zero Moment Point).

After setting a new gait parameter in STEP 3 as described above or whenit is not the switching timing of the gait in the above-mentioned STEP1, the controller 10 executes processing of STEP 4 and determines aninstantaneous desired gait as a desired gait in a current control cyclebased on a currently set gait parameter. That is to say, among thedesired gaits for one walking step of the robot 1 defined by thecurrently set gait parameters, the desired gaits (the desired positionand the posture of the upper body 2 at a current time t, the desiredposition and the posture of each foot mechanism 6, the desired totalfloor reaction force, and the desired ZMP) in the current control cycle(current time t) are determined as the instantaneous desired gaits.

Subsequently, the controller 10 executes control processing for acomposite-compliance operation in STEP 5, and corrects the desiredposition and the posture of each foot mechanism 6 in the instantaneousdesired gaits determined in STEP 4. In this processing for thecomposite-compliance operation, a moment component of the total floorreaction force (hereinafter referred to as a compensating total floorreaction force's moment) to be generated around the desired ZMP (anacting point of the desired total floor reaction force) to restore theupper body 2 into the desired posture depending on a deviation betweenthe desired posture of the upper body 2 (the desired inclination angle)and an actual inclination angle of the upper body 2 detected accordingto an output such as a gyro sensor, an acceleration sensor or the likewhich is not shown is determined. At this point, the compensating totalfloor reaction force's moment to be determined is a moment about an axisof a horizontal direction, and consists of a moment component about anaxis of a forward/backward direction of the robot 1 and a momentcomponent about an axis of a right/left direction. The controller 10then corrects the desired position and the posture of each footmechanism 6 such that a resultant force of the actual floor reactionforces (the actual total floor reaction force) for each leg 3 detectedby the six-axis force sensor 15 of each leg 3 follows a resultant forcebetween the above compensating total floor reaction force's moment andthe desired total floor reaction force within a range that a groundcontacting property of the foot mechanism 6 in a landing state can besecured. In this case, in the aforementioned desired ZMP as the actingpoint of the desired floor reaction force, the moment component aboutthe axis of the horizontal direction (the forward/backward direction andthe right/left direction) for the desired total floor reaction force is“0”. Accordingly, the corrections of the desired position and theposture of each foot mechanism 6 are performed to allow the momentcomponent about the axis of the horizontal direction for an actual totalfloor reaction force to follow the compensating total floor reactionforce's moment. Further, in such corrections of the desired position andthe posture of each foot mechanism 6, the desired position and theposture of each foot mechanism 6 is corrected so as to compensateinfluences of elastic deformations of the elastic member 16 and theground-contacting members 17 during the ground contact of each footmechanism 6.

Subsequently, the controller 10 executes control processing of thesolenoid valve 27 (STEP 6). This control processing is described later.

Subsequently, desired displacement amounts of respective joints 7through 9 of the two legs 3, 3 (more specifically, desired rotationalangles about each axis of respective joints 7 through 9) are determined(STEP 7) by kinematics arithmetic processing based on geometric modelsof the robot 1 (rigid link models) according to the desired position andthe posture of the upper body 2 of the instantaneous desired gaitsdetermined in the aforementioned STEP 4 and the desired position and theposture of each foot mechanism 6 corrected in STEP 5. The controller 10then controls torque of an electric motor (not shown) driving therespective joints 7 through 9 so as to allow actual displacement amountsof the respective joints 7 through 9 to follow the determined desireddisplacement amount (STEP 8). Further, in this situation, the actualdisplacement amounts of the respective joints 7 through 9 (actualrotational angles about each axis of respective joints 7 through 9) aredetected by rotary encoders or the like equipped in the respectivejoints 7 through 9. Moreover, the controller 10 increases a controlprocessing time t by a predetermined time At (time equivalent to aperiod of a control cycle) (STEP 9) to complete the processing of FIG.4.

According to the control processing of the controller 10 as has beendescribed, the robot 1 will move in such a way as to follow the desiredgaits while autonomously securing stability of its posture.

On the other hand, in the aforementioned STEP 6, the controller 10controls the solenoid valve 27 provided corresponding to the relevantleg 3 for each leg 3, as shown in a flowchart in FIG. 5.

According to the currently set gait parameters (the movement mode,length of step, movement speed of the robot 1 and the like), thecontroller 10 first sets compressed state holding time Thold whichdefines time (a period) when the bag-like member 19 is maintained in thecompressed state immediately after the leg 3 shifts from the landingstate to the lifting state, and valve opening time Topen which definestime (a period) when the solenoid valve 27 is controlled for openingafter releasing the maintenance of the compressed state (STEP 11). Inthis case, basically, as the movement speed of the robot 1 is higher,the compressed state holding time Thold is set at shorter time.Furthermore, basically, as the movement speed of the robot 1 isincreased, the valve opening time Topen is set at longer time. However,a sum of these compressed state holding time Thold and the valve openingtime Topen is shorter than time when the leg 3 is maintained in thelifting state.

Furthermore, the controller 10 determines time Tsup when the leg 3 is ina supporting leg stage (time when the foot mechanism 6 is maintained inthe state that the foot mechanism 6 is in contact with the groundthrough the ground-contacting members 17 or the bag-like member 19.Hereinafter, this is referred to as supporting leg time Tsup) based onthe currently set gait parameters (STEP 12).

Subsequently, the controller 10 judges whether or not the current time t(elapsed time from a switching point of the gait) is in a period of0≦t<Tsup+Thold, that is, whether or not it is in a period from a timewhen the bag-like member 19 of the foot mechanism 6 of the leg 3 almoststarts to make contact with the ground (a start time of the supportingleg stage) until the compressed state holding time Thold elapses afterthe supporting leg stage of the leg 3 ends (STEP 13). At this time, when0≦t<Tsup+Thold is satisfied, the controller 10 controls the solenoidvalve 27 for closing (STEP 14).

On the other hand, in STEP 13, when 0≦t<Tsup+Thold is not satisfied,that is, in the state after the compressed state holding time Tholdfurther elapses after the supporting leg stage of the leg 3 ends, thecontroller 10 judges whether or not the current time t satisfiesTsup+Thold≦t<Tsup+Thold+Topen (STEP 15). At this time, whenTsup+Thold≦t<Tsup+Thold+Topen is satisfied, the controller 10 controlsthe solenoid valve 27 for opening (STEP 16). Furthermore, whenTsup+Thold≦t<Tsup+Thold+Topen is not satisfied (in this case, basically,in the state little before the bag-like member 19 of the leg 3 againmakes contact with the ground by the landing motion of the leg 3 in thelifting state), the controller 10 controls the solenoid valve 27 forclosing (STEP 17).

By the above-described control of the solenoid valve 27, as shown in atiming chart in FIG. 6, the solenoid valve 27 is held closed in theperiod from the start time of the supporting leg stage of the leg 3until the compressed state holding time Thold elapses after thesupporting leg stage ends, including all the time of the supporting legstage. Accordingly, in this state, air in the atmosphere cannot flowinto the bag-like member 19. Furthermore, in a free leg stage of the leg3 (in a state that the entire foot mechanism 6 including the bag-likemember 19 is estranged from the floor A), the solenoid valve 27 is heldopened for the valve opening time Topen. In this state, the air in theatmosphere can flow into the bag-like member 19 through the fluidconduit 24.

Subsequently, an operation and an advantage of the landing shockabsorbing device 18 is described. During the movement of the robot 1 bythe aforementioned control processing of the controller 10, first thebag-like member 19 makes contact with the ground when the leg 3 on thefree leg side (the leg 3 in the lifting state) is landing. The bag-likemember 19 is compressed by a floor reaction force acting on the bag-likemember 19 with a progress of the landing motion of the leg 3.

At this moment, as the bag-like member 19 is compressed, the air in thebag-like member 19 is compressed and pressurized to be flowed outthrough the flow hole 21 and the fluid conduit 23. At this time, outflowresistance of the air is generated in the flow hole 21. Accordingly,motion energy of the leg 3 is damped. Additionally, in this situation, apart of the motion energy of the leg 3 is converted into and absorbed byelastic energy of the air according to spring property of the air ascompressible fluid. Furthermore, the elastic energy is dispersed by theoutflow resistance of the air from the bag-like member 19. Accordingly,while avoiding instantaneous rapid changes of the floor reaction forceacting on the leg 3 through the bag-like member 19, an impact load (alanding shock) in the landing motion of the leg 3 is reduced. In thissituation, the bag-like member 19 is deformable and is deformed along ashape of the floor A to be compressed, so that the landing shock may bereduced without suffering from so much influence by the shape of thefloor A and the posture of the foot mechanism 6 immediately beforelanding, and the bag-like member 19 is also less prone to damage and thelike.

The bag-like member 19 is compressed until the state that the footmechanism 6 makes contact with the ground through the front and rearground-contacting members 17 (the state that the landing motion of theleg 3 is completed).

Subsequently, although the bag-like member 19 attempts to inflate by itsown shape restoring force by the lifting motion of the leg 3, thesolenoid valve 27 is held closed until the compressed state holding timeThold elapses after the supporting leg stage of the leg 3 ends, asdescribed above. Therefore, not only in the state that the footmechanism 6 is in contact with the ground through the ground-contactingmembers 17 immediately after the lifting motion of the leg 3 starts butalso in the period from the time when the ground-contacting members 17are estranged from the floor A until the compressed state holding timeThold elapses, air in the atmosphere cannot flow into the bag-likemember 19. Accordingly, the bag-like member 19 does not inflate untilthe compressed state holding time Thold elapses after the foot mechanism6 shifts from the landing state to the lifting state.

In addition, after the foot mechanism 6 is completely estranged from thefloor A and the compressed state holding time Thold elapses, thesolenoid valve 27 is held opened for the valve opening time Topen. Atthis time, the bag-like member 19 is inflating by its own restoringforce to the natural state, while air in the atmosphere flows into thebag-like member 19 through the fluid conduit 24. In this case, the valveopening time Topen is set at shorter time than time required to inflatethe bag-like member 19 to the natural state. Accordingly, the height ofthe bag-like member 19 in the inflated state when the valve opening timeTopen elapses depends on the valve opening time Topen. Thus, in thestate that the bag-like member 19 inflates, the landing motion of theleg 3 is performed again, and the landing shock is reduced in thelanding motion as described above.

By the operation of the landing shock absorbing device 18 of the presentembodiment as explained above, the landing shock in the landing motionof each leg 3 can be reduced. In this case, according to the presentembodiment, in the landing state of the leg 3, air does not flow intothe bag-like member 19, so that the bag-like member 19 does not inflate.Therefore, the floor reaction force is not allowed to act on the portionof the bag-like member 19, but the floor reaction force is allowed tointensively act on a desired part of the foot mechanism 6 by the posturecontrol in the landing state of the foot mechanism 6. For example, whenthe robot 1 is about to fall forward, the floor reaction force can beconcentrated on the front end side of the foot mechanism 6. As a result,the posture stabilization of the robot 1 can be achieved easily. Forsupplemental description regarding this, if the solenoid valve 27 ismaintained opened in the landing state of the leg 3, air in theatmosphere attempts to flow into the bag-like member 19 (because thebag-like member 19 constantly attempts to inflate), so that the floorreaction force constantly acts on the portion of the bag-like member 19.Therefore, the floor reaction force cannot be concentrated on a desiredpart of the foot mechanism 6, and the posture stabilization of the robot1 by posture control in the landing state of the foot mechanism 6 is aptto be limited. In contrast, in the landing shock absorbing device 18 ofthe present embodiment, the limit of the posture stabilization of therobot 1 can be raised as described above.

Furthermore, since the bag-like member 19 is maintained in thecompressed state until immediately after the leg 3 shifts from thelanding state to the lifting state, when the foot mechanism 6 of the leg3 is estranged from the floor A, the bag-like member 19 does not inflateto make contact with the floor A. As a result, the lifting motion of theleg 3 can be performed smoothly without causing stumbling in the liftingmotion of the leg 3. In this case, since the time when the bag-likemember 19 is maintained in the compressed state immediately after theleg 3 shifts to the lifting state, that is, the compressed state holdingtime Thold is shorter as the movement speed of the robot 1 is faster, itcan be maintained to minimum time required. Thereafter, time forinflating the bag-like member 19 can be secured sufficiently.

Furthermore, according to the present embodiment, an upper limit of theheight of the bag-like member 19 when the bag-like member 19 inflates inthe lifting state of the leg 3, that is, the height of the bag-likemember 19 immediately before the landing motion of the leg 3 (this is asize of the bag-like member 19 in a compression direction) is defined bythe valve opening time Topen (the time when air is made to flow into thebag-like member 19). In addition, this valve opening time Topen is setaccording to the gait parameters, and basically, it is set at longertime as the movement speed of the robot 1 is faster. Therefore, as themovement speed of the robot 1 is faster, the height of the bag-likemember 19 immediately before the landing motion of the leg 3 is larger.Accordingly, as the movement speed of the robot 1 is faster, acompression amount of the bag-like member 19 in the landing motion ofthe leg 3 is larger. As a result, the reduction effect of the landingshock by the landing shock absorbing device 18 can be suitable for thegait type of the robot 1, and the landing shock can be smoothly reducedregardless of the gait type of the robot 1.

Additionally, the landing shock absorbing device 18 of the presentembodiment may bring the following effects. In other words, fluid thatflows into and out of the bag-like member 19 is the air as thecompressible fluid, and hence the landing shock absorbing device 18 maybe configured to be lightweight. Furthermore, during the landing motionof the leg 3, the pressure inside of the bag-like member 19 is increasedwith certain degree of a time constant and not increasedinstantaneously, so that the rapid change in the floor reaction forcemay be avoided. In addition, the air flowing out of the bag-like member19 when the bag-like member 19 is compressed is released into theatmosphere and new air flows into the bag-like member 19 from theatmosphere when the bag-like member 19 is inflated, and resultingly,heat generated with outflow resistance of the air from the bag-likemember 19 will not be stored in the bag-like member 19. In other words,the landing shock absorbing device 18 has a good heat dissipationproperty, so that a heat managing instrument such as an radiator doesnot need to be provided.

Additionally, the spring constant of the air in the bag-like member 19functioning as a spring during the landing motion of the leg 3 becomessmall with the compression immediately after the bag-like member 19makes contact with the ground, and hence an effect of control of theaforementioned composite-compliance operation may be enhanced. That isto say, in the control of the composite-compliance operation of therobot 1, as described above, the position and the posture of each footmechanism 6 are corrected so as to allow the moment component about theaxis of the horizontal direction for the actual total floor reactionforce (hereinafter referred to as an actual total floor reaction force'smoment) to follow the compensating total floor reaction force's moment(also including an occasion that the compensating total floor reactionforce's moment is “0”) as a desired value of the moment component. Sucha composite-compliance operation control is for making the landingposition and the posture of the foot mechanism 6 adjust to the floor Ato secure the stability of the posture of the robot 1, even when thefloor A has an inclination. In this situation, in order to enhance afollowing-property of the actual total floor reaction force's moment tothe compensating total floor reaction force's moment, it is preferablethat a compliance gain in the composite-compliance operation control,that is, a change amount of the desired landing position and the postureof the foot mechanism 6 to a change of the deviation between the actualtotal floor reaction force's moment and the compensating total floorreaction force's moment (a change amount of the rotational angle of theankle joint 9) is increased. However, when the above compliance gain istaken to be big, in general, a loop gain of the composite-complianceoperation control (generally, this is proportional to the product of theabove compliance gain and the total spring constant of the springmechanism which the foot mechanism 6 has (the ground-contacting members17, the elastic member 16, and the landing shock absorbing device 18))becomes big, and resultantly, a control system tends to be unstable.

However, the spring constant of the air in the bag-like member 19 of thelanding shock absorbing device 18 of the present embodiment becomessmall with the compression immediately after the bag-like member 19makes contact with the ground, and hence the above loop gain becomessmall. As a result, even when the compliance gain is increased, thestability of the composite-compliance operation control may be secured.Consequently, the following-property of the actual total floor reactionforce's moment to the compensating total floor reaction force's momentmay be improved and furthermore, the securement of the stability of theposture of the robot 1 may be improved.

Subsequently, referring to FIG. 7, a second embodiment of the presentinvention is described. FIG. 7 is a flowchart for explaining anoperation of a substantial part of the present embodiment. Further, thepresent embodiment differs from the first embodiment only in a part ofcontrol processing of the solenoid valve 27, so that the referencenumerals identical to those of the first embodiment are used.Descriptions about component portions identical to those of the firstembodiment are omitted.

According to the first embodiment, the opening and closing timing of thesolenoid valve 27 is determined based on time information only. However,when actual ground-contacting timing in the landing motion of the leg 3of the robot 1 (timing at which the bag-like member 19 of the footmechanism 6 makes contact with the ground) falls behind a scheduledtime, the controller 10 positively lets down the foot mechanism 6 torapidly land the leg 3 on the floor. This is apt to cause a largerlanding shock than usual in the landing motion of the foot mechanism 6.

The present embodiment is intended to address such a situation, and thecontroller 10 controls the solenoid valve 27 in STEP 6 of FIG. 4 asshown in the flowchart of FIG. 7. That is to say, according to thepresent embodiment, in STEPs 21 and 22, the controller 10 executes thesame processing as that in STEPs 11 and 12 of FIG. 5 according to thefirst embodiment, and then in STEP 23, the controller 10 judges whetheror not the current time t satisfies 0≦t<Tsup, that is, whether or notthe current time t is within the supporting leg stage of the leg 3. Atthis time, in the case of 0≦t<Tsup, the controller 10 further judgeswhether or not the foot mechanism 6 of the leg 3 is actually in contactwith the ground through the ground-contacting members 17 or the bag-likemember 19 (STEP 24). This judgment is made based on output of thesix-axis force sensor 15, for example. In addition, in STEP 24, when thefoot mechanism 6 is in contact with the ground, the solenoid valve 27 iscontrolled for closing (STEP 25). Alternatively, in STEP 24, when thefoot mechanism 6 is not in contact with the ground, the solenoid valve27 is controlled for opening (STEP 26).

Furthermore, when the current time t does not satisfy 0≦t<Tsup in STEP23, the controller 10 then executes the same judgment processing as thatin STEP 15 of the FIG. 5 according to the first embodiment, that is,whether or not the current time t satisfiesTsup+Thold≦t<Tsup+Thold+Topen in STEP 27. Then, according to thisjudgment result, in STEP 28 or 29, the opening and closing control ofthe solenoid valve 27 is executed as in the first embodiment. In thiscase, according to the present embodiment, a state thatTsup+Thold≦t<Tsup+Thold+Topen is not satisfied in STEP 27 includes astate of Tsup≦t<Tsup+Thold. Accordingly, in the state ofTsup≦t<Tsup+Thold, in STEP 29, the solenoid valve 27 is controlled forclosing as in the first embodiment.

By the aforementioned opening and closing control of the solenoid valve27, when the foot mechanism 6 is in contact with the ground through theground-contacting members 17 or the bag-like member 19 in the supportingleg stage of the leg 3, that is, when the lifting/landing motions of theleg 3 are being performed as scheduled according to a desired gait, theopening and closing control of the solenoid valve 27 is performedcompletely similar to the first embodiment. Accordingly, in this case,an operation and an effect by the landing shock absorbing device 18 ofthe present embodiment are the same as those of the first embodiment.

On the other hand, when the foot mechanism 6 is not in contact with theground through the ground-contacting members 17 or the bag-like member19 in the supporting leg stage (0≦t<Tsup), that is, for example, in suchan occasion that the bag-like member 19 is not in contact with theground at the time when the bag-like member 19 of the leg 3 should havemade contact with the ground in the landing motion of the leg 3, thesolenoid valve 27 is controlled for opening. In this case, the solenoidvalve 27 is not necessarily required to be completely opened, and it maybe controlled for half-opening, for example.

In this manner, since the solenoid valve 27 is controlled for opening,the bag-like member 19 resumes the inflation that has been ceased byclosing the solenoid valve 27 when the valve opening time Topen elapsesin the lifting state of the leg 3, so that air flows into the bag-likemember 19 to thereby increase the height of the bag-like member 19. As aresult, even when the foot mechanism 6 is lowered in order to rapidlybring the foot mechanism 6 of the leg 3 into contact with the ground,the landing shock of the leg 3 can be reliably reduced.

Subsequently, a third embodiment of the present invention is describedreferring to FIGS. 8 and 9. FIG. 8 is an exemplary view of a substantialpart of a foot mechanism provided with a landing shock absorbing deviceof the present embodiment, and FIG. 9 is a flowchart for explaining anoperation of the substantial part of the present embodiment. Accordingto the present embodiment, the foot mechanism is the same as that of thefirst embodiment except for a configuration relating to the landingshock absorbing device, and only a substantial configuration of the footmechanism is illustrated in FIG. 8. Furthermore, in the descriptions ofthe present embodiment, for the same component portions or the samefunctional portions as those of the first embodiment, the referencenumerals identical to those of the first embodiment are used, anddescriptions are omitted.

Referring to FIG. 8, according to the present embodiment, a plate member28 is fixedly provided at a bottom face portion inside of the bag-likemember 19 attached to a bottom face of the foot plate member 12, and arod member 29 extended upward from this plate member 28 slidablypenetrates the foot plate member 12 in the vertical direction (thecompression direction of the bag-like member 19) to project to an upperside of the foot plate member 12. Accordingly, a length of theprojecting portion of the rod member 29 (hereinafter, referred to as aprojection amount) becomes larger as the bag-like member 19 iscompressed, depending on the height of the bag-like member 19. Inaddition, on the projection portion of the rod member 29, there isloaded a linear potentiometer 30 as a sensor for detecting theprojection amount and thus the height of the bag-like member 19 (thesize of the bag-like member 19 in the compression direction), and anoutput signal of this linear potentiometer 30 is input to the controller10 so that the opening and closing control of the solenoid valve 27 ofthe inflow/outflow means 20 having the same configuration as that of thefirst embodiment is performed by the controller 10. Configurations otherthan the foregoing (including the control processing of the controller10 other than the opening and closing control of the solenoid valve 27)are the same as those of the first embodiment.

Furthermore, according to the present embodiment, in STEP 6 of FIG. 4,the controller 10 controls the solenoid valve 27 as shown in theflowchart of FIG. 9. That is to say, the controller 10 first sets thecompressed state holding time Thold described in the first embodimentand a desired value of an upper limit height Hcmd of the bag-like member19 when inflating the bag-like member 19 in the lifting state of the leg3 (hereinafter, referred to as a desired inflation height Hcmd),according to the currently set gait parameters (the movement mode,length of step, movement speed of the robot 1, etc.) (STEP 31). In thiscase, the way to set the compressed state holding time Thold is the sameas that of the first embodiment. Furthermore, basically, the desiredinflation height Hcmd is set at a larger value as the movement speed ofthe robot 1 is higher. However, according to the present embodiment, thedesired inflation height Hcmd is a height equal to or less than a heightin the natural state of the bag-like member 19.

Furthermore, the controller 10 determines the supporting leg time Tsupwhen the leg 3 is in the supporting leg stage based on the currently setgait parameters as in STEP 12 of FIG. 5 in the first embodiment (STEP32).

Subsequently, the controller 10 judges whether or not the current time t(the elapsed time from the switching point of the gait) is within theperiod of 0≦t<Tsup+Thold (STEP 33). At this time, in the case of0≦t<Tsup+Thold, the controller 10 controls the solenoid valve 27 forclosing (STEP 34). The processing in STEPs 33 and 34 is the same as thatin STEPs 13 and 14 in FIG. 5 of the first embodiment.

On the other hand, in STEP 33, when 0≦t<Tsup+Thold is not satisfied, thecontroller 10 further detects an actual height Hact of the bag-likemember 19 in the current bag-like member 19 by the output of the linearpotentiometer 30 (STEP 35) to compare this detected height Hact with theaforementioned desired inflation height Hcmd (STEP 36). In addition, inthe case of Hact<Hcmd, the controller 10 controls the solenoid valve 27for opening (STEP 37), and in the case of Hact≧Hcmd, the controller 10controls the solenoid valve 27 for closing (STEP 38).

By the above-described closing and opening control of the solenoid valve27, the bag-like member 19 is maintained in the compressed state, in thelanding state of the leg 3 and immediately after shifting from thelanding state to the lifting state, which is completely similar to thefirst embodiment.

On the other hand, according to the present embodiment, during theinflation of the bag-like member 19 after opening the solenoid valve 27in the lifting state of the leg 3, when the actual height Hact of thebag-like member 19 becomes the desired inflation height Hcmd setaccording to the gait parameters, the solenoid valve 27 is controlledfor closing to block off the inflow of air into the bag-like member 19.As a result, the height of the bag-like member 19 before landing of therobot 1 is controlled to be the desired inflation height Hcmd.Accordingly, similar to the first embodiment, a reduction effect of thelanding shock by the landing shock absorbing device 18 can be suitablefor the gait type of the robot 1, and the landing shock can be smoothlyreduced regardless of the gait type of the robot 1. In addition, in thiscase, since the height of the bag-like member 19 is reliably controlledto be the desired inflation height Hcmd according to the gait type ofthe robot 1, the reduction effect of the landing shock can beadvantageously secured.

Subsequently, a fourth embodiment of the present invention is describedreferring to FIG. 10. FIG. 10 is a flowchart for explaining an operationof a substantial part of the present embodiment. Since the presentembodiment differs from the third embodiment only in a part of thecontrol processing of the solenoid valve 27, reference numeralsidentical to those of the first embodiment are used. In addition,descriptions of component portions identical to those of the thirdembodiment are omitted.

According to the present embodiment, similar to the second embodiment,an occasion where the foot mechanism 6 of the leg 3 makes contact withthe ground behind the scheduled time is considered. The controller 10controls the solenoid valve 27 in STEP 6 of the FIG. 4 as shown in theflowchart of FIG. 10. That is to say, in STEPs 41 and 42, the controller10 executes the same processing as the processing in STEPs 31 and 32 ofFIG. 9 in the third embodiment, and then in STEP 43, the controller 10judges whether or not the current time t satisfies 0≦t<Tsup, that is,whether or not the current time t is within the supporting leg stage ofthe leg 3. At this time, in the case of 0≦t<Tsup, the controller 10further judges whether or not the foot mechanism 6 of the leg 3 isactually in contact with the ground through the ground-contactingmembers 17 or the bag-like member 19 thereof (STEP 44). This judgment ismade based on the output of the six-axis force sensor 15, for example.In addition, in this STEP 44, when the foot mechanism 6 is in contactwith the ground, the solenoid valve 27 is controlled for closing (STEP45).

When the foot mechanism 6 is not in contact with the ground in STEP 44,the controller 10 increases the currently set desired inflation heightHcmd (STEP 46). In this case, an increase amount of the desiredinflation height Hcmd is, for example, a predetermined unit increaseamount. Furthermore, the controller 10 detects the actual height Hact ofthe bag-like member 19 for the current bag-like member 19 by the outputof the linear potentiometer 30 (STEP 47) to compare this detected heightHact with the desired inflation height Hcmd (STEP 48). Then, in the caseof Hact≧Hcmd, the controller 10 controls the solenoid valve 27 foropening (STEP 49), and in the case of Hact≧Hcmd, the controller 10controls the solenoid valve 27 for closing (STEP 45).

On the other hand, in STEP 43, when the current time t does not satisfy0≦t<Tsup, the controller 10 then judges whether or not the current timet satisfies Tsup≦t<Tsup+Thold (STEP 50). At this time, in the case ofTsup≦t<Tsup+Thold, the controller 10 controls the solenoid valve 27 forclosing (STEP 51). Alternatively, when Tsup≦t<Tsup+Thold is notsatisfied, the controller 10 executes the aforementioned processing fromSTEP 47 to control the solenoid valve 27 for opening and closing basedon the comparison of the actual height Hact and the desired inflationheight Hcmd of the bag-like member 19.

By the opening and closing control of the solenoid valve 27 as describedabove, when the foot mechanism 6 is in contact with the ground throughthe ground-contacting members 17 or the bag-like member 19 in thesupporting leg stage of the leg 3, that is, when the lifting/landingmotions of the leg 3 are performed as scheduled according to the desiredgait, the opening and closing control of the solenoid valve 27 isperformed completely similar to the third embodiment. Accordingly, inthis case, an operation and an effect by the landing shock absorbingdevice 18 of the present embodiment are the same as those the thirdembodiment.

On the other hand, when the foot mechanism 6 is not in contact with theground through the ground-contacting members 17 or the bag-like member19 in the supporting leg stage of the leg 3 (0≦t<Tsup), that is, forexample, when the bag-like member 19 is not in contact with the groundat a time when the bag-like member 19 of the leg 3 should have madecontact with the ground in the landing motion of the leg 3, the desiredinflation height Hcmd is increased to control the solenoid valve 27 foropening. At this time, the opening of the solenoid valve 27, that is,the inflow of air into the bag-like member 19 is performed until theactual height of the bag-like member 19 becomes the increased desiredinflation height Hcmd. This inflates the bag-like member 19 so that theheight of the bag-like member 19 becomes larger than the heightaccording to the original gait type. However, according to the presentembodiment, since the air flowing into the bag-like member 19 is air inthe atmosphere, the upper limit of the height of the bag-like member 19during inflation is the height in the natural state of the bag-likemember 19.

In this manner, when the bag-like member 19 of the leg 3 is not incontact with the ground at the time when the bag-like member 19 of theleg 3 should have made contact with the ground in the landing motion ofthe leg 3, air is flowed into the bag-like member 6 to increase theheight of the bag-like member 19, so that the landing shock of the leg 3can be reliably reduced even if the foot mechanism 6 is lowered in orderto rapidly bring the foot mechanism 6 of the leg 3 into contact with theground.

The height Hact of the bag-like member 19, being detected by the linearpotentiometer 30 according to the third and fourth embodiments, may bedetected by a distance-measuring sensor using laser beam or the like.Furthermore, since pressure inside of the bag-like member 19 duringinflation, in general, has correlation with the height of the bag-likemember 19, the pressure inside of the bag-like member 19 may be detectedby a pressure sensor to perform the opening and closing control of thesolenoid valve 27 based on the detected pressure, thereby controllingthe height of the bag-like member 19 during inflation.

Furthermore, although according to the above-described first throughfourth embodiments, the air inflow into the bag-like member 19 iscontrolled through the solenoid valve 27 in order to maintain thebag-like member 19 in the compressed state or in order to control theheight of the bag-like member 19 during inflation, for example,mechanical means as shown in FIG. 11 or electromagnetic means as shownin FIG. 12 may be used in order to control the inflation and compressionof the bag-like member 19. In FIGS. 11 and 12, substantial parts of thefoot mechanisms 6 are illustrated as in FIG. 8.

In the example shown in FIG. 11, as in the third embodiment, a platemember 31 is fixedly provided at the bottom face portion inside of thebag-like member 19, and a rod member 32 extending upward from this platemember 31 slidably penetrates the foot plate member 12 in the verticaldirection (the compression direction of the bag-like member 19) toproject to the upper side of the foot plate member 12. In addition, onthe rod member 32, there is loaded a one-way clutch mechanism 33, whichenables the rod member 32 to freely move in the compression direction ofthe bag-like member 19 (the direction in which the rod member 32 movesup), and the rod member 32 to be locked by a command given by thecontroller 10 or the like in the inflation direction of the bag-likemember 19 (the direction in which the rod member 32 moves down). In thecase where such a mechanism is provided, the rod member 32 is maintainedlocked by the one-way clutch mechanism 33 from after the bag-like member19 enters the compressed state by the landing motion of the leg 3 (afterthe foot mechanism 6 makes contact with the ground through the front andrear ground-contacting members 17) until immediately after the leg 3shifts from the landing state to the lifting state (the timing when thesolenoid valve 27 is switched from the closing state to the openingstate immediately after shifting into the lifting state in the firstthrough fourth embodiments), whereby the bag-like member 19 can bemaintained in the compressed state as in the first through fourthembodiments. In this case, locking the rod member 32 enables thebag-like member 19 to more reliably be maintained in the compressedstate. Furthermore, in the lifting state of the leg 3, the rod member 32is locked by the one-way clutch mechanism 33 at the timing of switchingthe solenoid valve 27 from the opening state to the closing stateaccording to the first through fourth embodiments, thereby more reliablycontrolling the height of the bag-like member 19 to be a desired height.

Furthermore, in the example shown in FIG. 12, at the bottom face portioninside of the bag-like member 19, there is fixedly provided a plate-likemagnetic element 34, and at an upper face portion inside of the bag-likemember 19 (at a lower face portion of the foot plate member 12) there isfixedly provided an electromagnet 35. In the case where suchelectromagnetic means is provided, adsorptivity is generated withrespect to the magnetic element 34 by the electromagnet 35 from afterthe bag-like member 19 enters the compressed state by the landing motionof the leg 3 (after the foot mechanism 6 makes contact with the groundthrough the front and rear ground-contacting members 17) untilimmediately after the leg 3 shifts from the landing state to the liftingstate (the timing when the solenoid valve 27 is switched from theclosing state to the opening state immediately after shifting to thelifting state in the first through fourth embodiments), thereby morereliably maintaining the bag-like member 19 in the compressed state.

Subsequently, a fifth embodiment of the present invention is describedreferring to FIGS. 13 through 15. FIG. 13 is an exemplary view showing asubstantial part of a foot mechanism provided with a landing shockabsorbing device of the present embodiment, FIG. 14 is a flowchart forexplaining an operation of the substantial part of the presentembodiment, and FIGS. 15 are timing charts for explaining the operationof the present embodiment. According to the present embodiment, the footmechanism is the same as that of the first embodiment except for theconfiguration relating to the landing shock absorbing device, and inFIG. 13, only the substantial configuration of the foot mechanism isillustrated. Furthermore, in the descriptions of the present embodiment,for the same component portions or functional portions as those of thefirst embodiment, reference numerals identical to those of the firstembodiment are used, and descriptions are omitted.

Referring to FIG. 13, the landing shock absorbing device 18 of thepresent embodiment is provided with inflow/outflow means 37 made of afluid conduit 35 led out from the bag-like member 19 side incommunication with the interior portion of the bag-like member 19attached to the bottom face of the foot plate member 12, and aproportional solenoid valve 36 which is provided at this fluid conduit35 and whose opening can be controlled by the controller 10.Furthermore, a pressure sensor 38 is provided inside of the bag-likemember 19 and a distance-measuring sensor 39 detecting the height of thebag-like member 19 is further provided on the foot plate member 12. Thedistance-measuring sensor 39 detects the height of the bag-like member19 using laser beam, for example. Outputs of these sensors 38 and 39(detection signals) are input into the controller 10. Configurationsother than the foregoing are completely similar to those of the firstembodiment.

Furthermore, according to the embodiment, the control processing of thecontroller 10 differs from the first embodiment only in the processingin STEP 6 of FIG. 4, and in this STEP 6, the proportional solenoid valve36 is controlled for each leg 3 as shown in the flowchart of FIG. 14.

Specifically, the controller 10 first judges whether or not the currenttime t satisfies t=0, that is, whether or not starting timing of thesupporting leg stage of the leg 3 (STEP 61) is presented, and in thecase of t=0, patterns of change with time of a desired pressure Pcmdinside of the bag-like member 19 and change with time of a desiredheight HHcmd of the bag-like member 19 are set according to the currentgait parameters (STEP 62). In this case, the patterns of the desiredpressure Pcmd and the desired height HHcmd are, for example, set asshown in FIGS. 15A and 15B, respectively.

More specifically, the desired height HHcmd is set so as to monotonouslydecrease from an initial value HHcmd0 to “0” in a period Ta immediatelyafter start of the supporting leg stage (immediately after groundcontact of the bag-like member 19 of the foot mechanism 6) (the periodTa is basically a period until the foot mechanism 6 completely makescontact with the ground through the front and rear ground-contactingmembers 17). Then, in a period Tb from time when the period Ta elapsesuntil the early free leg stage of the leg 3 (immediately after the legshifts from the landing state to the lifting state), the desired heightHHcmd is maintained at “0”. HHcmd=0 denotes a height of the bag-likemember 19 in the state that the foot mechanism 6 makes contact with theground through the front and rear ground-contacting members 17 and thatthe bag-like member 19 is completely compressed. Furthermore, from timewhen the period Tb elapses until the free-leg stage ends, the desiredheight HHcmd is increased to a predetermined value HHcmd1 and in theend, maintained at the predetermined value HHcmd1. Here, thepredetermined value HHcmd1 is equivalent to the desired height Hcmd inthe third and fourth embodiments. Furthermore, the initial value HHcmd0of the desired height HHcmd at start time of the supporting leg stage isequivalent to the final desired height HHcmd (HHcmd1) in the free legstage before the supporting leg stage. In this case, the final desiredheight HHcmd1 in the free leg stage, a length of the period Tb, and thelike are set according to the movement speed of the robot 1 or the likeas in the first through fourth embodiments.

Furthermore, basically, the desired pressure Pcmd is set so as totemporarily increase from “0”, and then to decrease to “0” in the periodTa in the early supporting leg stage of the leg 3. In addition, afterthe period Ta elapses, Pcmd=0 is maintained until the free leg stageends. Pcmd=0 denotes that the pressure inside of the bag-like member 19is equivalent to the atmospheric pressure. In this case, a maximum valueand the like of the desired pressure Pcmd in the free leg stage are setaccording to the gait parameters, and basically, as the movement speedof the robot 1 is higher, the maximum value of the desired pressure Pcmdis set at a larger value.

After setting the patterns of change with time of the desired pressurePcmd and the desired height HHcmd, as described above, or when t=0 isnot satisfied in STEP 1, the controller 10 determines an instantaneousdesired pressure Pcmd and an instantaneous desired height HHcmd at thecurrent time t based on the above patterns (STEP 63).

Subsequently, the controller 10 detects an actual pressure Pact insideof the bag-like member 19 by the pressure sensor 38, and the actualheight Hact of the bag-like member 19 by the distance-measuring sensor39 (STEP 64), and thereafter, the controller 10 judges whether or notthe foot mechanism 6 is in contact with the ground through the bag-likemember 19 or the ground-contacting members 17 (STEP 65). This judgmentis made based on, for example, a detected value of the actual pressurePact by the six-axis force sensor 15 or the pressure sensor 38.

When the foot mechanism 6 is in contact with the ground, the controller10 controls the opening of the proportional solenoid valve 36 based onthe instantaneous desired pressure Pcmd and the instantaneous desiredheight HHcmd determined in STEP 63, and the actual pressure Pact insideof the bag-like member 19 and the actual height Hact of the bag-likemember 19 detected in STEP 64 (STEP 66). In this case, the controller 10determines the opening of the proportional solenoid valve 36(hereinafter, referred to as valve opening), for example, by thefollowing formula (1) to control the proportional solenoid valve 36 forthe determined valve opening.Valve opening=k1·(Pact−Pcmd)+k2·(Hact−HHcmd)  (1)

Here, k1 and k2 in the formula (1) are predetermined positive gaincoefficients. In addition, when a calculation result on the right-handside of the formula (1) is a negative value, the valve opening isforcefully set at “0” (valve closing state of the proportional solenoidvalve 36).

Furthermore, in STEP 65, when the foot mechanism 6 is not in contactwith the ground, the controller 10 controls the opening of theproportional solenoid valve 36 based on the instantaneous desired heightHHcmd determined in STEP 63 and the actual height Hact of the bag-likemember 19 detected in STEP 64 (STEP 67). In this case, the controller 10determines the valve opening, for example, by the following formula (2)to control the proportional solenoid valve 36 for the determined valveopening.Valve opening=−k3·(Hact−HHcmd)  (2)

Here, k3 in the formula (2) is a predetermined positive gaincoefficient. In addition, when a calculation result on the right-handside of the formula (2) is a negative value, the valve opening isforcefully set at “0” (valve closing state of the proportional solenoidvalve 36).

In the ground-contacting state of the foot mechanism 6 (including thebag-like member 19), that is, in the supporting leg stage of the leg 3,the above-described control of the valve opening of the proportionalsolenoid valve 36, in other words, the control of air inflow into thebag-like member 19 enables the actual pressure Pact inside of thebag-like member 19 and the actual height Hact of the bag-like member 19to basically vary so as to generally follow the patterns of the desiredpressure Pcmd and the desired height HHcmd, respectively. Furthermore,in the state that the foot mechanism 6 is not in contact with theground, that is, in the free leg stage of the leg 3, the actual heightHact of the bag-like member 19 varies so as to follow the pattern of thedesired height HHcmd. In this case, since the pattern of the desiredheight HHcmd is set as described above, the bag-like member 19 isbasically maintained in the compressed state from after the compressionby the landing motion of the leg 3 until immediately after the leg 3shifts from the landing state to the lifting state. Furthermore, in thefree leg stage of the leg 3, the bag-like member 19 inflates to theheight according to the gait parameters defining the gait type of therobot 1. Accordingly, the same operation and effect as those of thefirst embodiment can be brought about. Furthermore, according to thepresent embodiment, in the ground-contacting state of the foot mechanism6, the actual pressure Pact inside of the bag-like member 19 is alsocontrolled so as to generally follow the desired pressure Pcmd accordingto the gait parameters, so that a reduction effect of the landing shockby the landing shock absorbing device 18 can be suitable for the gaittype of the robot 1.

Although according to the present embodiment, in the ground-contactingstate of the foot mechanism 6, the valve opening of the proportionalsolenoid valve 36 is determined by the formula (1), the valve openingmay be determined, for example, by the following formula (3) or (4).Valve opening=k1·(Pact−Pcmd)−k2·HHcmd  (3)Valve opening=−k1·Pcmd+k2·(Hact−HHcmd)  (4)

When using these formulas (3) and (4), in the supporting leg stage ofthe leg 3, basically, the actual pressure Pact inside of the bag-likemember 19 and the actual height Hact of the bag-like member 19 can alsobe varied to generally follow the patterns of the desired pressure Pcmdand the desired height HHcmd, respectively.

Although according to the present embodiment, the patterns of thedesired pressure Pcmd and the desired height HHcmd are set, for example,only the pattern of the desired height HHcmd may be set to control theproportional solenoid valve 36 so as to allow the actual height Hact ofthe bag-like member 19 to follow the set pattern. In this case, ineither of the supporting leg stage and the free leg stage, the valveopening of the proportional solenoid valve 36 may be determined, forexample, by the formula (2).

Although according to the first through fifth embodiments as describedabove, the bag-like member 19 is provided at the bottom face side of thefoot plate member 12, the bag-like member 19 may be provided, forexample, between the foot plate member 12 and the ankle joint 9. Anembodiment of this case is described as a sixth embodiment referring toFIG. 16. FIG. 16 is a cross-sectional view of a side face of a footmechanism provided with a landing shock absorbing device of the presentembodiment. Since the present embodiment differs from the firstembodiment only in a part of configuration of the foot mechanism and apart of configuration of the landing shock absorbing device, for thesame component portions or functional portions as those of the firstembodiment, the same reference numerals identical to those of the firstembodiment are used and descriptions are omitted.

According to the present embodiment, in an upper face portion of thefoot mechanism 6, the tube member 13 in a cross-sectionally rectangularform is fixedly provided as in the first embodiment, and inside of thetube member 13, there is housed the bag-like member 19 (a variablecapacity element) having an upwardly opened barrel shape similar to thebag-like member of the first embodiment. In this case, the bottom faceportion of the bag-like member 19 is firmly fixed to the foot platemember 12 inside of the tube member 13. Furthermore, inside of the tubemember 13, movable tube member 40 with a bottom is housed on an upperside of the bag-like member 19, and this movable tube member 40 isdisposed movably along an inner circumferential surface of the tubemember 13 in the vertical direction. In addition, an opening end of thebag-like member 19 is fixedly provided at a bottom portion of themovable tube member 40. Accordingly, the movable tube member 40 isjoined to the foot plate member 12 through the bag-like member 19.Furthermore, two flow holes 41 and 42 are drilled at the bottom portionof the movable tube member 40 communicatively with the interior portionof the bag-like member 19. These flow holes 41 and 42 are throttledpassages.

Furthermore, inside of the movable tube member 40, there is housed amovable plate 43 which can move in the substantially vertical directionalong an inner circumferential surface of the movable tube member 40,and the movable plate 43 is connected to the bottom portion of themovable tube member 40 through a plurality of elastic members 44(described as a spring in the figure) with a peripheral portion of itslower face constructed of a spring, rubber, or the like. In addition,the ankle joint 9 of the leg 3 is connected to an upper face portion ofthis movable plate 43 through the six-axis force sensor 15.

Furthermore, the inflow/outflow means 20 including the flow holes 41 and42 are provided. This inflow/outflow means 20 is the same as that of thefirst embodiment in basic configuration, comprising the fluid conduit 23connected to, and led out from the fluid hole 41, the check valve 25provided in this fluid conduit 23, the fluid conduit 24 connected to,and led out from the fluid hole 42, and the check valve 26 and thesolenoid valve 27 provided in this fluid conduit 24. In addition, farend portions of the fluid conduits 23 and 24 are opened to theatmosphere side. The landing shock absorbing device 18 of the presentembodiment is constructed of this inflow/outflow means 20 and thebag-like member 19.

According to the present embodiment, the bag-like member 19 isconstructed of an elastic material which is hard to stretch more thanthe inflation state shown in the figure (the natural state) to preventthe movable tube member 40 from falling off from the tube member 13 dueto the bag-like member 19 extended by weight of foot plate member 12 andthe like in the lifting state of the leg 3. Alternatively, the movabletube member 40 is structurally adapted not to fall off from the tubemember 13. Configurations other than the foregoing (including thecontrol processing of the controller 10) are identical to those of thefirst embodiment.

In the landing shock absorbing device 18 of the present embodimentconfigured as described above, in the landing motion of the leg 3, whenthe foot mechanism 6 of the leg 3 makes contact with the ground throughthe ground-contacting members 17, air inside of the bag-like member 19flows out through the flow hole 41 while compressing the bag-like member19. At this time, since the flow passage 41 is a throttled passage,outflow resistance occurs. Such an operation of the landing shockabsorbing device 18 of the present embodiment reduces the landing shockin the landing motion of the leg 3 as in the first and the secondembodiments. Furthermore, by the opening and closing control of thesolenoid valve 27 similar to the first embodiment, the bag-like member19 is maintained in the compressed state from after the compression ofthe bag-like member 19 until immediately after the foot mechanism 6shifts from the landing state to the lifting state. Moreover, in thelifting state of the foot mechanism 6, the bag-like member 19 inflatesto a desired height. This can bring about the same operation and effectas those of the first embodiment.

Although according to the present embodiment, the control of air inflowinto the bag-like member 19 is performed similar to the firstembodiment, air inflow into the bag-like member 19 can also becontrolled similar to the second through fourth embodiments.

Furthermore, although according to the present embodiment, the bag-likemember 19 is provided as a variable capacity element, it is possiblethat the tube member 13 is formed into a cylindrical (cylindertube-like) shape for example, that the movable tube member 40 is formedinto a piston form, and that the bag-like member 19 is configured as avariable capacity element in a space under the movable tube member 40inside of the tube member 13.

Furthermore, although according to the first through sixth embodiments,the fluid flowing in and out with respect to the variable capacityelement is air, the fluid may be a liquid such as hydraulic oil in thepresent invention.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide a landing shockabsorbing device which can easily secure posture stability of a leggedmobile robot such as a biped mobile robot while reducing an impact loadduring a landing motion of a leg of the robot, and further, which can beconfigured to be lightweight.

1. A landing shock absorbing device of legged mobile robot moving bylifting and landing motions of a plurality of legs that can make contactwith the ground though a ground-contacting face portion of a footmechanism, respectively, the landing shock absorbing device comprising:a variable capacity element provided in the foot mechanism of each leg,each variable capacity element being compressed by undergoing a floorreaction force during the landing motion of an associated leg and beinginflatable when no longer undergoing the floor reaction force at leastby the lifting motion of the associated leg, thereby allowing fluid toflow into the variable capacity element with the inflation thereof andto flow out of an interior portion of the variable capacity element withthe compression thereof, and an inflow/outflow means for communicatingthe fluid into the variable capacity element while inflating thevariable capacity element in a lifting state of the associated leg andfor communicating the fluid out of the variable capacity element withthe compression of the variable capacity element caused by the floorreaction force, wherein outflow resistance is generated during theoutflow of the compressible fluid in the variable capacity element bythe inflow/outflow means, the landing shock absorbing device comprisinginflation control means for controlling an inflow amount of the fluidinto the variable capacity element by the inflow/outflow means dependingon the gait type to change a size of the variable capacity element in acompression direction to become a predetermined size depending on a gaittype of the legged mobile robot, when the variable capacity element isinflated in the lifting state of the associated leg, wherein thevariable capacity element is constructed of a deformable bag-like memberprovided on a bottom face side of the foot mechanism of the associatedleg to make contact with the ground ahead of the ground-contacting faceportion of the foot mechanism of the associated leg during the landingmotion of said associated leg.
 2. The landing shock absorbing deviceaccording to claim 1, further comprising a sensor for detecting aphysical quantity that varies depending on a size of the variablecapacity element in the compression direction, wherein the inflationcontrol means judges whether the size of the variable capacity elementin the compression direction is inflated to a predetermined size basedon detection data of the sensor, and when the size of the variablecapacity element in the compression direction is judged to be inflatedto the predetermined size, blocks the inflow of the fluid into thevariable capacity element by the inflow/outflow means.
 3. The landingshock absorbing device according to claim 1, further comprising a sensorfor detecting whether or not the foot mechanism of each of the legs isin contact with the ground, wherein the inflation control means controlsthe inflow of the fluid into the variable capacity elements associatedwith each of the legs by the inflow/outflow means to increase the sizeof the variable capacity elements in the compression direction, when aground-contact of the foot mechanism is not detected by the sensor at aplanned time for landing each leg defined depending on desired gaits ofthe legged mobile robot.
 4. A landing shock absorbing device of leggedmobile robot moving by lifting and landing motions of a plurality oflegs that can make contact with the ground though a ground-contactingface portion of a foot mechanism, respectively, the landing shockabsorbing device comprising: a variable capacity element provided in thefoot mechanism of each leg, each variable capacity element beingcompressed by undergoing a floor reaction force during the landingmotion of an associated leg and being inflatable when no longerundergoing the floor reaction force at least by the lifting motion ofthe associated leg, thereby allowing fluid to flow into the variablecapacity element with the inflation thereof and to flow out of aninterior portion of the variable capacity element with the compressionthereof, and an inflow/outflow means for communicating the fluid intothe variable capacity element while inflating the variable capacityelement in a lifting state of the associated leg and for communicatingthe fluid out of the variable capacity element with the compression ofthe variable capacity element caused by the floor reaction force,wherein outflow resistance is generated during the outflow of thecompressible fluid in the variable capacity element by theinflow/outflow means, the landing shock absorbing device comprisinginflation control means for controlling an inflow amount of the fluidinto the variable capacity element by the inflow/outflow means dependingon the gait type to change a size of the variable capacity element in acompression direction to become a predetermined size depending on a gaittype of the legged mobile robot, when the variable capacity element isinflated in the lifting state of the associated leg, wherein theinflation control means judges whether a size of the variable capacityelement in a compression direction is inflated to a predetermined sizebased on inflow time of the fluid into the variable capacity element inthe lifting state of the associated leg, and when the size of thevariable capacity element is judged to be inflated to the predeterminedsize, blocks the inflow of the fluid into the variable capacity elementby the inflow/outflow means.
 5. The landing shock absorbing deviceaccording to claim 4, further comprising a sensor for detecting aphysical quantity that varies depending on a size of the variablecapacity element in the compression direction, wherein the inflationcontrol means judges whether the size of the variable capacity elementin the compression direction is inflated to a predetermined size basedon detection data of the sensor, and when the size of the variablecapacity element in the compression direction is judged to be inflatedto the predetermined size, blocks the inflow of the fluid into thevariable capacity element by the inflow/outflow means.
 6. The landingshock absorbing device according to claim 4, further comprising a sensorfor detecting whether or not the foot mechanism of each of the legs isin contact with the ground, wherein the inflation control means controlsthe inflow of the fluid into the variable capacity elements associatedwith each of the legs by the inflow/outflow means to increase the sizeof the variable capacity elements in the compression direction, when aground-contact of the foot mechanism is not detected by the sensor at aplanned time for landing each leg defined depending on desired gaits ofthe legged mobile robot.
 7. A landing shock absorbing device of leggedmobile robot moving by lifting and landing motions of a plurality oflegs that can make contact with the ground though a ground-contactingface portion of a foot mechanism, respectively, the landing shockabsorbing device comprising: a variable capacity element provided in thefoot mechanism of each leg, each variable capacity element beingcompressed by undergoing a floor reaction force during the landingmotion of an associated leg and being inflatable when no longerundergoing the floor reaction force at least by the lifting motion ofthe associated leg, thereby allowing fluid to flow into the variablecapacity element with the inflation thereof and to flow out of aninterior portion of the variable capacity element with the compressionthereof; an inflow/outflow means for communicating the fluid into thevariable capacity element while inflating the variable capacity elementin a lifting state of the associated leg and for communicating the fluidout of the variable capacity element with the compression of thevariable capacity element caused by the floor reaction force; and asensor for detecting a size of the variable capacity element in thecompression direction, wherein outflow resistance is generated duringthe outflow of the compressible fluid in the variable capacity elementby the inflow/outflow means, wherein the landing shock absorbing devicecomprises an inflation control means for controlling an inflow amount ofthe fluid into the variable capacity element by the inflow/outflow meansdepending on the gait type to change a size of the variable capacityelement in a compression direction to become a predetermined sizedepending on a gait type of the legged mobile robot, when the variablecapacity element is inflated in the lifting state of the associated leg,and wherein the inflation control means sets a time-varying pattern of adesired size of the variable capacity element in the compressiondirection depending on the gait type of the legged mobile robot at atime that the variable capacity element is inflated, and controls theinflow and the outflow of the fluid of the variable capacity element bythe inflow/outflow means such that the size of the variable capacityelement in the compression direction detected by the sensor is changedaccording to the time-varying pattern of the desired size.
 8. Thelanding shock absorbing device according to claim 7, further comprisinga sensor for detecting a physical quantity that varies depending on asize of the variable capacity element in the compression direction,wherein the inflation control means judges whether the size of thevariable capacity element in the compression direction is inflated to apredetermined size based on detection data of the sensor, and when thesize of the variable capacity element in the compression direction isjudged to be inflated to the predetermined size, blocks the inflow ofthe fluid into the variable capacity element by the inflow/outflowmeans.
 9. The landing shock absorbing device according to claim 7,further comprising a sensor for detecting whether or not the footmechanism of each of the legs is in contact with the ground, wherein theinflation control means controls the inflow of the fluid into thevariable capacity elements associated with each of the legs by theinflow/outflow means to increase the size of the variable capacityelements in the compression direction, when a ground-contact of the footmechanism is not detected by the sensor at a planned time for landingeach leg defined depending on desired gaits of the legged mobile robot.